1. Field of the Invention
The invention relates to the production of glycoside compositions by reacting starch hydrolysates with glycols and triols in the presence of strong acid catalysts and more particularly relates to such glycoside compositions which are subsequently treated to lower their reducing sugar content.
2. Other Methods in the Field of the Invention
Carbohydrate-based polyols derived from starch are well known. It is also established that such polyols are useful in the preparation of polyurethane foams as seen in U.S. Pat. No. 3,073,788.
A reducing sugar, such as the simple aldose or glycose sugars, exists primarily in a cyclic hemiacetal form. In the presence of acid catalysts, hemiacetals react with alcohols to give acetals. ##STR1##
The expression ROH may be a simple alcohol, a glycol, or even another carbohydrate unit. Since polysaccharides such as starch are made up of acetal-linked monosaccharide units, their acid-catalyzed hydrolysis or transglycosidations are also represented by the chemistry expressed in the above equation.
U.S. Pat. No. 3,165,508 to Otey, et al. teaches that degraded starch glycoside polyoxyalkylene ether compositions, useful for reaction with organic diisocyanates, are prepared by reacting unmodified starch with polyols such as ethylene glycol, propylene glycol or glycerol under specific temperature conditions in the presence of a strong mineral acid, followed by etherification with a 1,2-alkylene oxide. Fuzesi suggests introducing the 1,2-alkylene oxide into the reaction mixture of the starch, polyhydric alcohol and acid according to U.S. Pat. No. 3,277,213.
Polyols have also been made from reducing sugars directly by addition of the sugars to an alkylene oxide in the presence of a base as disclosed by Molotsky in U.S. Pat. No. 3,600,338. Unfortunately, the reducing sugars present are sensitive to alkaline catalysts and undergo a variety of condensation and degradation reactions, some of which produce undesirable color. Glycol ethers have also been used to react with cornstarch in a transglycosylation (similar to a transesterification, etc.). Again, the resulting intermediate is alkoxylated to give a starch-based polyol useful in making polyurethanes according to U.S. Pat. No. 3,721,665 to Moss, et al.
U.S. Pat. No. 3,772,269 to Lew teaches glycoside compositions prepared from the reaction of starch hydrolysates, monosaccharides or polysaccharides, with monoalcohols and alkylene glycols of 3 to 5 carbon atoms over an acid catalyst. The ultimate glycoside compositions are useful as detergents, gelling agents, lubricants, wetting agents, dyeing assistants, textile softeners and food emulsifiers.
The orthoformic esters found to be useful in the invention herein are known to function in at least four different ways in the presence of reducing sugars, alcohols or glycols, water and acid catalysts.
First, orthoformic esters may function as water scavengers as taught by G. Kesslin and R. Bradshaw in "Ortho Esters as Water Scavengers," I & EC Product Research and Development, Vol. 5, No. 1, 1966, pp. 27-29 according to the following scheme ##STR2##
The ester may also react with the free aldehyde to form an acetal, a common technique in protecting aldehyde groups. The following scheme suggested by J. F. W. McOmie in Protective Groups in Organic Chemistry, Plenum Press, London, 1973, pp. 327-328 may be postulated ##STR3##
Further, the ester could conceivably react with the hemiacetal in a reaction such as ##STR4##
Finally, the ester could exchange with excess alcohol or glycol. ##STR5##
In all of the formulas given previously R, R', R" and R"' simply stand for different alkyl groups.
Reactions of carbohydrates with 2,2-dimethoxypropane to give various products have been performed subsequent to my invention. For example, M. Kiso, et al. in Carbohydrate Research, 1976, Vol. 52(1), pp. 87-101 disclose the reaction of 2,2-dimethoxypropane with compounds such as D-glucose, D-xylose, D-arabinose and D-ribose to give a wide variety of products, see Chemical Abstracts 86: 140362v, 1977. Acetals such as 4-O-(3,4-O-isopropylidene-.beta.-D-galactopyranosyl)-2,3.dbd.5,6-di-O-isop ropylidene-1,1-di-O-methyl-D-glucose may be made by reacting together compounds such as lactose, p--CH.sub.3 C.sub.6 H.sub.4 --SO.sub.3 H and 2,2-dimethoxypropane by exchange acetalation according to L. Thelwall, et al. in European Pat. No. 17,397 as noted in Chemical Abstracts 94: 121877r, 1981. The reaction of maltose with 2,2-dimethoxypropane can give 1,2-O-isopropylidene-.alpha.-maltose, 4-O-.alpha.-D-glucopyranosyl-2,3.dbd.5,6-di-O-isopropylidene-D-glucose aldehydrol and 1,2.dbd.4',6'-di-O-isopropylidene-.alpha.-maltose as taught by Y. Ueno, et al. in Carbohydrate Research, 1981, Vol. 89(2), pp. 271-278 as found in Chemical Abstracts 95: 25433t, 1981.
There is still a need for a method of lowering the proportion of reducing sugars in various glycoside compositions so that the eventual polyol and polyisocyanate are as free from color as possible.